It is well understood in the vacuum furnace art that a "piece" or "work piece", which has been subjected to the high temperatures of the furnace, should be cooled in some positive way and that such a positive technique is the cooling or quenching of the hot work piece in an atmosphere of an inert gas such as nitrogen or argon. The hot work piece is normally not cooled in air because it is usually desirable that oxidation not take place. Hence an inert gas such as nitrogen is used. It becomes apparent that if relatively rapid cooling is desired, then the inert gas should be continuously passed over and in contact with the hot work piece, to remove heat, and then purged from the hot zone enclosure and replaced by cooled inert gas which in turn will remove further heat from the work piece.
In the prior art this technique has been accomplished by designing and employing steel pipes which are fitted and mounted around the outside periphery of the hot zone enclosure. Such pipes are further formed to have offshoots, or protrusions, which are fitted through holes in the outside wall of the hot zone enclosure. It has generally been the practice, in the prior art, to employ more than one such pipe with a hot zone enclosure and the plurality of offshoots or smaller pipes form a plurality of inlet members within the hot zone enclosure. With this arrangement, in the prior art, inert gas is fed into the main pipes, through the offshoot pipes, into the hot zone enclosure to surround the hot work piece. This prior art arrangement has worked satisfactorily for the most part but has created problems when the need for maintenance arises. As the maintenance problems were carefully studied it was discovered that not only could they be solved but that an improved means for providing inert gas would also result.
In the prior art, as mentioned above, the main pipes are mounted through suitable brackets or otherwise to the hot zone enclosure. If the hot zone enclosure has to be removed for repairs, it becomes necessary to first remove the pipes in order to remove the hot zone enclosure from the furnace chamber. The pipes and in particular the offshoot pipes are awkward to handle and very often because they become brittle, with constant expansion and contraction, they tend to break. If an offshoot pipe breaks, it means that the entire assembly has to be removed because the offshoot pipes are made integral with the main pipe assembly. In addition the mounting structure per se is awkward to handle.
Besides the awkwardness and capacity for breakage, it is well understood that there are pressure losses through such pipe systems and hence the distribution of the gas into the hot zone enclosure is non uniform.
The present gas duct arrangement eliminates any necessity to remove any duct-like structure if it becomes necessary to remove the hot zone enclosure. In addition the present gas duct arrangement enables the system to provide a uniform distribution of the quenching gas in the hot zone enclosure and enables a lower operating gas pressure than in the prior art.